Drainage unit having a quilt exterior

ABSTRACT

A substantially cylindrical drainage unit for use when buried in soil as part of a wastewater leach field comprises a first plastic aggregate mass that is contained within netting, with an optional central perforated pipe. A segmented quilt comprises the exterior surface of the drainage unit which is in contact with soil. Pebble aggregate that is smaller in particle size than the first aggregate is contained with the cavities of the quilt segments. Quilts having different segment shapes and sizes are manufactured by specialized apparatus which creates rectilinear or serpentine seams.

This application claims benefit of provisional patent application Ser.No. 61/845,801, filed Jul. 12, 2013.

TECHNICAL FIELD

The present invention relates to drainage units which may be used inwastewater disposal systems and other underground systems for gatheringor dispersing water.

BACKGROUND

It is long been common to flow wastewater issuing from septic tanks ofsubsurface wastewater treatment systems to rows of structures buried intrenches within the soil, generally called leaching fields. Olderleaching field systems comprise a crushed stone-filled trench with alengthwise running pipe. More modern systems include prefabricateddrainage units which are placed in trenches back-filled with stone andsoil. One kind of such drainage unit comprises a generally cylindricalshape mass of plastic bead aggregate which is contained within in asleeve of netting. Typically, a perforated pipe runs down the center ofthe mass of aggregate to distribute wastewater along the length of thedrainage unit.

A familiar commercial example of such a unit is an EZflow® drainageunit, sold by Infiltrator Systems, Inc. The units are easily handled byinstallers and may be placed in straight or curved trenches. Typically,downward infiltration of soil or other overlying material into theinterstices of the aggregate of a drainage unit is inhibited by use of apermeable geotextile fabric that is either laid on top of the unit afterplacement, or that has been attached to or integrated with the exteriorof the unit. For instance, geotextile may be attached to the sleevewhich retains the aggregate or may be a component of the sleeve. SeeU.S. Pat. No. 6,854,924 and U.S. Pat. No. 8,256,990 for examples. Whensuch geotextile is part of a manufactured drainage unit the geotextilelayer has been referred to as a barrier.

During use, wastewater flows outwardly from a drainage unit into thesurrounding soil, sand or gravel. If the rate of inflow exceeds the rateof outflow into the surrounding soil, wastewater will be stored in theinterstices of the aggregate. Much attention had been paid by designers,installers, repairmen and regulators to what happens at the interfacebetween the drainage unit exterior surface and the surrounding soil orother medium. A so-called biomat is often observed at interfaces betweena wastewater leaching unit and surrounding soil. When a drainage unitcomprises a geotextile barrier, suspended solids in the wastewater canbuild up on the barrier, when they are too large to pass through theopenings in the fabric of the barrier. That can inhibit the flow ofwater from the drainage unit into the surrounding soil. Thus, it hasbeen considered by some that it is a disadvantage, or at least notnecessary, to run a geotextile barrier all around the outer surface of adrainage unit, since geotextile is primarily needed to preventinfiltration of soil at the top, and to a lesser degree the sides.Generally, there is a continuing effort to enhance the performance ofdrainage units with respect to treatment of wastewater and avoidingdegradation over time of use.

SUMMARY

An object of the invention is to provide an aggregate type drainage unitthat is useful for leaching system application, in particular a unitwhich has improved soil-interface characteristics or improved capacityfor handling suspended solids. A further object of the invention is toprovide a method and apparatus for making drainage units having surfaceregions with enhanced wastewater treatment properties, in particularexteriors which comprise finer aggregates and increased surface area.

In accord with the invention, an embodiment of drainage unit comprises agenerally cylindrical mass of first plastic aggregate (particulate)which is circumscribed by a quilt made of geotextile fabric. The quiltcomprises a multiplicity of segments having cavities filled with secondplastic aggregate (pebbles) which are smaller in size and larger insurface area than the first aggregate. An optional perforated pipe runsalong the length of the mass of first plastic aggregate, and when thepipe is present the quilt is secured by ties to the exposed pipe ends. Apreferred quilt comprises two layers of fabric, with the innermost layerbeing more water permeable than the outermost layer. A preferred quiltconstruction presents an undulating surface to the surrounding soil; thesurface area per unit length of the drainage unit exterior is at least1-2 percent, and preferably a least up to 7 percent, greater in than thesurface area per unit length of a same-size drainage unit having asmooth geotextile surface, as characterizes prior art units. A quiltprovides the exterior region of a drainage unit with a wastewatertreatment region which is different that which exists within the firstaggregate. The ability of a drainage unit to handle suspended solids isenhanced.

In an embodiment of the invention the first aggregate is kept in placeas a cylindrical mass by means of a quilt which is in the form of asleeve. In another embodiment, the first aggregate is contained by afirst sleeve of netting, as in the prior art; and the quilt wraps aroundthat assembly (which is called here an essential drainage unit). Thequilt may be fabricated in the form of a rectangular blanket which isthen wrapped around the essential drainage unit and secured to itself.Alternatively, a second sleeve of netting which circumscribes theexterior of the wrapped-around quilt and keeps it in place. In otherembodiments of the invention, a quilt runs only partially around thecircumference of a drainage unit.

In embodiments of the invention the quilt comprises a base layer ofgeotextile and a cap layer of geotextile which are attached to eachother at seams. The cap layer is a layer which becomes the mostcontoured most during fabrication of a quilt; and it has the greaterundulating surface in the finished quilt. Either the cap layer or thebase layer may be in closest proximity to the first aggregate mass of adrainage unit. The layer which is closest to the first aggregate masspreferably has a higher permeability than the other layer; and usuallythere is higher stiffness and lesser undulation associated with thelower permeability geotextile layer which presents as the exterior ofthe drainage unit.

Quilt geotextile layers are joined to each other by a multiplicity ofseams which define the quilt segments. The quilt segments may havedifferent shapes, including lengthwise strips, rectangles, or curvedportions. Preferably, the quilt segments are rectangles defined by acombination of longitudinal seams and transverse seams (relative to thelengthwise axis of the drainage unit). Preferably rectangular quiltsegments are oriented relative to each other so that the transverserunning seams align and form as circumferential bands that facilitatebending of a drainage unit in order to fit within a curved trench insoil during use.

Drainage units having quilts may be in part fabricated in differentways, including by joining together two geotextile layers at seams bymeans of sewing, ultrasonic welding, fusion welding, etc. to form atwo-layer quilt structure. In one approach, the sheet layers are runhorizontally while aggregate is deposited within the cavities of thequilt segments being formed. Preferably, rectilinear quilt segments areformed by means a combination of lengthwise and transverse movingfastening heads. Serpentine seams may run within parallel lengthwiseband regions. In another method of quilt formation, the fabric layersare mated and seamed—preferably by ultrasonic welding—so there arecreated vertical channels between downwardly moving layers within afabricating apparatus. Pebble aggregate is dropped into upper ends ofthe vertical channels preferably by a shuttle mechanism which meters theamount of aggregate. A horizontal seam is then formed just above theelevation of aggregate after it is deposited in a vertical channel, tocreate a desired rectangular segment.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent from the following description ofpreferred embodiments and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective partial-cutaway view of a drainage unit of thepresent invention which has a central flow distribution pipe andcomprises an exterior surface which is a segmented quilt.

FIG. 2 is a diametrical cross section through the drainage unit shown inFIG. 1.

FIG. 2A is a cross section through the quilt, in flattened condition, ofthe drainage unit of FIG. 1,

FIG. 3 is a fragmentary view of the cross section shown in FIG. 2, toprovide more detail.

FIG. 4 is an elevation cross section view showing three drainage unitsof FIG. 1 in a sand filled trench of a leaching field.

FIG. 5 is a fragmentary view like that of FIG. 3, showing a drainageunit with a quilt having the base layer of the quilt as the exteriorsurface, with a resultant a lesser amount of undulation than has thequilt shown in FIG. 3.

FIG. 6 is top view showing a portion of the rectangular-segmented quiltof the FIG. 1 drainage unit, as it is being fabricated in flatconfiguration by use of heads which fasten the fabric sheets of thequilt together.

FIG. 7 is a view like FIG. 6, showing a quilt with nominally circularquilt segments along with stylized sewing heads, to illustrate a methodof making the quilt.

FIG. 7A is a view like FIG. 7, showing a quilt with serpentine seamswhich intersect each other to define oblong segments.

FIG. 7B is a view like FIG. 7, showing a quilt with serpentine seamswhich cross each other to make complex shape segments.

FIG. 8 is a view like FIG. 6, showing a portion of a quilt havingsegments which are lengthwise strips.

FIG. 9 is a perspective simplified view of apparatus for forming aquilt, along with a quilt in the process of being fabricated. The quiltmoves horizontally during fabrication, when aggregate is captured inchannels between the mating geotextile sheets of the quilt.

FIG. 10 is a side elevation cross section of the apparatus and quiltshown in FIG. 9.

FIG. 10A is a fragmentary view of a modification of the apparatus shownin FIG. 9, wherein aggregate is deposited within the channels of abeing-formed quilt by means of tubes.

FIG. 11 is a fragmentary view showing a modification of the FIG. 9apparatus, in particular, where sewing heads are staggered apart in thedownstream direction.

FIG. 12 is a partial top view of quilt structure produced by theapparatus of FIG. 9, showing where the structure can be cut intoindividual quilts for incorporation into a drainage unit.

FIG. 13 is a diametrical cross section of a drainage unit being formed,showing how a quilt may be wrapped around the exterior of an essentialdrainage unit so the ends overlap.

FIG. 13A is a diametrical cross section of a drainage unit having aquilt which only partially goes around the circumference of the unit.The drainage unit also lacks a central pipe.

FIG. 14 is a diametrical cross section of a drainage unit comprisingaggregate contained within a sleeve, a circumscribing geonet, andcircumscribing geotextile (compared to a quilt) around the exteriorsurface of the geonet.

FIG. 15 is a vertical cross section view of a portion of apparatus forforming a quilt, where the quilt moves vertically during fabrication.

FIG. 16 is a partial cross section through a roller of the FIG. 15apparatus.

FIG. 17 shows an exemplary product produced by the apparatus of FIG. 15.

FIG. 18 is a view like FIG. 15, showing a modification of apparatus formaking quilt.

FIG. 19 is a perspective partial-cutaway view like FIG. 1, showing adrainage unit where the quilt is secured to the exterior by a sleeve ofnetting.

FIG. 19A is a partial cross section through the drainage unit shown inFIG. 19.

FIG. 20 is a vertical cross section through a mandrel from which a quiltsleeve is payed off onto a perforated pipe moving through the mandrel,also showing how aggregate blown down the bore of the mandrel fills thequilt.

FIG. 21 shows a mandrel like that in FIG. 1 along with a quilt as it isbeing fed onto the mandrel and edge-fastened so it becomes a sleeve likethat shown in FIG. 20.

FIG. 22 is a cross section of a mandrel holding nicked sleeve nettingshowing how an essential drainage unit is formed in accord with theprior art.

DESCRIPTION

FIG. 1 is a perspective view of an exemplary drainage unit 20 of thepresent invention comprising a quilt-exterior. FIG. 2 is a partialdiametrical cross section of drainage unit 20. FIG. 2A a portion of thequilt only in flattened condition. In use, drainage units 20 areconnected end to end to form a string, and strings of units aretypically arranged as parallel spaced apart rows in a leaching field.The term “drainage unit” is used for simplicity here and should not beconsidered limiting. The term comprehends units which are useful fortreating and dispersing wastewater in soil, for storing and dispersingrainwater in soil or, alternatively, for gathering water from saturatedsoil. A preferred embodiment of the invention is described below interms of the use of the invention in connection with treatment ofwastewater. Other uses of drainage unit of the present invention includedispersing other liquids within permeable particulate masses, andcollecting liquids from same when they are saturated.

Drainage unit 20 is an improvement over prior art drainage units whichunits may be incorporated as portions of embodiments of the presentinvention. Reference may be made to the drainage unit described in U.S.Pat. No. 5,015,123 and U.S. Pat. No. 6,497,031, both of Houck et al. andthe methods of making described therein. The disclosures of theforegoing patents are hereby incorporated by reference.

An essential drainage unit, as the term is used herein, is a referenceto that portion of the present invention which is made in accord withthe teachings of the foregoing patents or which is comparable to unitswhich are presently known in commerce. An embodiment of essentialdrainage unit 16 which is a portion of exemplary drainage unit 20 shownin FIG. 1 is generally cylindrical in shape and typically will be 8 to12 inches in diameter and 10 feet in length. A mass of plastic aggregate26, preferably polystyrene beads, is contained within a sleeve 24 madeof plastic netting which has openings small enough to contain theaggregate. As known in the prior art, the netting generally presents ashaving diamond shape openings; other shape openings may be used. Asillustrated and described below, the netting of sleeves used in thepresent invention may be generally characterized as having uniform sizeopenings. In the generality of the invention, a sleeve of netting mayhave openings which vary in size, including that a portion of the sleevemade of netting may comprise an integral or attached geotextile barrieras described in prior art patents, including U.S. Pat. No. 8,256,990 ofKoerner, the disclosure of which is hereby incorporated by reference.

Aggregate 26 is preferably expanded polystyrene that is about ¾ inch to1¼ inch in dimension and has a ribbed shape like that shown in U.S. Pat.No. 6,467,996 of Garner, the disclosure of which is hereby incorporatedby reference. Perforated pipe 22, preferably a common flexiblecorrugated plastic drainage pipe, runs lengthwise along axis L of thedrainage unit, through the center of the aggregate 26. In the generalityof the invention, the pipe may be off-center. The presence of the pipeis optional in the generality of the invention.

The essential drainage unit 16 and the whole drainage unit 20 arereferred to herein as being generally cylindrical and as havingdiameters. These terms should be construed loosely and appliedreasonably on a nominal basis, since the nature of the non-rigidmaterials involved means that the drainage units may have irregular,e.g., oblong, cross sections and the nominal diameters of cross sectionsmay vary along the length of a unit. Embodiments of the invention maycomprehend units having non-round cross sections, for instancerectangular cross sections. Presently, those cross sections would bemore difficult to make.

In accord with the present invention, quilt 30 forms the exteriorsurface of the drainage unit 20. The exemplary quilt 30 of unit 20 iscomprised of two layers 32, 34 of water permeable fabric which areattached to each other in a way which defines a multiplicity ofnominally rectangular, preferably square, segments 43. The exteriorsurface of the drainage unit 20 is uneven and undulating due to theseams which define the quilt segments. Thus the drainage unit 20presents to a surrounding particulate medium more surface area than ispresented when a drainage unit of the same exterior diameter has anexterior surface that comprises a layer of geotextile without quilting,as in the prior art. The segments 43 are defined by lengthwise seams 44and transverse seams 48 which are preferably aligned as shown so thatseams 48 circumscribe the drainage unit. As described below, other shapequilt segments may be used. Each quilt segment 43 has an interior cavityfilled with a second aggregate 36, often called pebbles herein.

FIG. 3 is a more detailed view of a portion of the drainage unit crosssection shown in FIG. 2 and FIG. 2A is a detail view of the quilt byitself. From both Figures it can be seen that quilt 30 is comprised totwo layers of geotextile, namely base layer 34 and cap layer 32, whichare attached to each other at seams. The terminology “base” and “cap” isreflective of the manner in which the quilt is typically formed, but theterminology should not be considered as limiting. In a preferred quiltfabrication process, the cap layer is contoured with lengthwise peaksand valleys prior to or during the seaming process by which it isattached to the base layer. After a quilt is formed the base layer willtend to have a contoured surface, as an effect of the seams. Indifferent embodiments either the cap layer or the base layer may presenton the exterior of the drainage unit.

The layer of a quilt which presents as the exterior of a drainage unitwill be made of a geotextile which is sufficiently durable to withstandmechanical and environmental stresses during handling, installation anduse of the drainage unit. A lesser performance material—and thereforeoften lighter weight material—can be used as the layer of the quiltwhich faces toward the center of the drainage unit. Thus it will beappreciated that the lighter-weight layer will typically be moresubstantially contoured than the other layer. As described below, indifferent embodiments of the invention, either the cap layer or the baselayer may present toward the exterior of a drainage unit.

In the FIG. 3 embodiment, the base layer 34 of the quilt is in contactwith netting sleeve 24 and any aggregate which lies within the spacingof the ligaments of the netting of the sleeve. The mesh size of thesleeve netting is large relative to the size of the beads of aggregate26, but sufficient to retain it. Sleeve 24 will typically allow portionsof aggregate to protrude a bit through the openings of the netting, ascharacterizes prior art essential drainage units. For purposes ofclarity of illustration, the thicknesses and radial spacing of layers32, 34 are exaggerated. See representative dimensions of an exemplarydrainage unit, discussed below.

Contained within the space between the two fabric layers 32, 34 is asecond aggregate, namely aggregate 36, called here pebbles 36 toemphasize a distinction with the preferably coarser beads of firstaggregate 26. (Nonetheless, in the generality of the invention, a firstaggregate might be nominally the same size as the second aggregate.)Pebbles 36 are preferably short expanded polystyrene cylinders, shapedlike pills, with both a diameter and length of about one-quarter inch(about 6 mm) and a density of about 0.7 to 1.2 pounds per cubic foot(about 11.2 to 19.2 kilogram per cubic meter). Generally, a quilt isthin compared to the thickness of the first aggregate mass, since thequilt is principally concerned with wastewater treatment near theexterior surface of the drainage unit, whereas the first aggregate masshas a primary function of providing a space within the earth for storageand distribution of water. A typical quilt thickness will be betweenabout three-eighth and five-eighth inch (about 1 cm and 1.6 cm). See theexample below.

Referring to FIG. 3 and drainage unit 20, the essential drainage unit 16portion has a diameter D1 and has an associated cylindrical surface areaper unit length, called A1. D3 is the diameter of an imaginary cylindercircumscribing the exterior of the unit 20. D2 is the average diameterof the quilt, i.e., the average of diameters D1 and D3, having anassociated cylindrical surface area per unit length, called A2. Theundulating exterior surface of the drainage unit 20 formed by fabric 32thus has a surface area per unit length which is greater than thesurface area per unit length A1, A2 or A3 which would be provided by adrainage unit having a un-quilted exterior surface comprising the samefabric which characterizes layer 32 or layer 34. A reference to thesurface area per unit length is a reference to the property whichcharacterizes the central fifty percent of the drainage unit; that is,the effects of the contours and distortions of a quilt toward each endof the drainage unit are ignored in the calculation.

An essential drainage unit having a diameter D1, with geotextile lyingon the surface provided by the aggregate 26 and netting 24, may havesome unevenness reflective of the unevenness of the aggregate whichprotrudes through the spaces of the netting of sleeve 24, but in contextof the present invention is will be considered as being substantiallysmooth. By way of example, an exemplary invention drainage unit 20comprises an about 10.7 inch (27 cm) diameter (D1) exemplary essentialdrainage unit 16. The exemplary unit 20 comprises a circumscribing quilt32 of about five-eighth inch (about 1.6 cm) thickness, and thus the unit20 has a diameter (D3) of nominally 12 inches (30.5 cm).

The seams of exemplary quilt are about one quarter inch (about 0.6 cm)wide at the location where the two layers of geotextile are attached toeach other. An exemplary quilt 32 shown in FIG. 8 has long rectangularstrip-like segments where the seams are about 4.5 inch (about 11.5 cm)spaced apart. The exemplary quilt 30 shown in FIG. 1 has square segmentsabout 4.5 inch square. The segments are about five-eighth inch thickmidway between the seams.

An exemplary drainage unit in accord with the invention has a quiltsurfaced exterior which has a surface area per unit length that is atleast 1-2 percent, preferably about 5-7 percent or more, greater thanthe surface area per unit length of a smooth surface (un-quilteddrainage) unit. When the quilt has nominally square segments or curvedor round segments as described herein, the undulation and surface areaadvantage can be greater than when the segments are lengthwise(rectangular) strips. The greater surface area of the invention drainageunit provides an advantage in usefulness by increasing the area ofparticulate medium (e.g., sand or gravel or soil) which is in contactwith the exterior of the drainage unit. So, to the extent the leachingcapacity of a drainage unit is limited by the permeability or flow rateof the geotextile or by the surface area of the soil or other mediumwhich is in contact with fluid flow openings on the exterior of thedrainage unit, then the invention will offer an advantage over the priorart. Typical embodiments of drainage units may have diameters between 10and 12 inch (25 and 30 cm) and a nominal length of 10 feet (2.5 meter),or as desired.

While an undulating exterior quilt surface is preferred for the reasonsjust given, within the scope of invention a drainage unit embodiment mayhave a quilt surface which is substantially smooth. As noted elsewhere,such a quilt provides other wastewater treatment benefits, relating tothe aggregate surface area of the quilt, as described elsewhere herein.FIG. 5 shows, as an example, quilt 30B of drainage unit 20B, where thean exterior base layer 32B is has less undulation than the inner caplayer 34B This FIG. 5 configuration of drainage unit is representativeof a unit which may be made using a quilt produced by the methoddescribed in connection with FIGS. 15-18. It is also an example of howquilt may be configured in an embodiment of the drainage unit shown inFIGS. 19 and 19A.

For practical cost and weight reasons, and for resisting corrosion, theaggregate 36 is a non-metallic material, preferably plastic. Optionallya ceramic such as vermiculite or ceramic foam may be used. As mentioned,a preferable material of aggregate is expanded polystyrene, well-knownin the art for such purpose. Other plastics which may be used includepolyethylene and polypropylene.

FIG. 4 illustrates by example how a drainage unit 20 is used. FIG. 4 isa transverse cross section through natural soil 40 in which has been duga trench 38, now filled with sand 42. In the example, there are threeparallel drainage units 20 embedded in the sand. Backfill soil 40Acovers the sand 42. During a typical use, when the drainage units 20 arepart of a wastewater leaching system, wastewater from a source such as aseptic tank is distributed by means a distribution box or the like, notshown, to the perforated conduits or pipes 22 of the three drainageunits 20. During use, water flowing into pipes 22 flows fromperforations in the pipe wall into the interstices of bead aggregate 26.The water flows radially outward from pipe 22, typically with a downwardbias when the sand 42 is not water-saturated. The water then passesthrough netting 24, through geotextile base layer 34 of the quilt, intothe pebbles 36 of the quilt; then through the geotextile cap layer 32;then into the surrounding sand 42 or such other material as may surroundthe drainage units in other installations; and, finally into the soil40. In alternative embodiments, there is no sand and drainage units 20are surrounded within the trench by backfilled natural soil,alternatively by crushed stone gravel instead of sand.

In a typical prior art drainage unit, after wastewater is initiallyreceived and stored within the interstices of the larger-bead aggregate26, it passes through the netting of the sleeve and then through thefabric of any barrier layer adjacent to the sleeve and then into thesurrounding medium. In prior art units the barrier layer may runpartially or all around the drainage unit. See U.S. Pat. No. 8,256,990of Koerner. While the geotextile barrier is intended to preventinfiltration of soil and the like into the bead aggregate, as pointedout in the Background a geotextile barrier can be a location wheresuspended solids in the wastewater accumulate and might inhibit flow.

In an exemplary drainage unit of the present invention, the wastewaterhas to pass through the aggregate/pebbles of the quilt 30 beforeentering the surrounding medium such as sand 42, except where there arenecessary seams. Thus the wastewater flowing through a drainage unit 20of the present invention may be filtered as it passes successivelythrough the base layer 34 and the cap layer 32, and it is subject tomicrobiological treatment while passing through the interstices amongstpebbles 36.

The average particle size of the aggregate 36 in the quilt is preferablysubstantially smaller than the average particle size of the aggregate 26that is contained within sleeve 24. Average particle size is determinedby conventional means when, as is the case here, the plastic particlesare irregular. If, in an example of the invention, the average particlesize of the pebble 36 aggregate in the sleeve is one-quarter inch, andthe average particle size of the aggregate 26 in the sleeve is one inch,then the ratio of quilt-aggregate to sleeve-aggregate particle size toless than 1 to 2, being 1 to 4.

The surface area per unit volume of the pebbles 36 is desirablysubstantially greater than the surface area per unit volume of the beadsof aggregate 26; preferably at least 1.5 times greater. One calculationof shows exemplary pebbles of the second aggregate within the quiltprovide about 55-60 percent more surface area per unit volume than dothe exemplary beads of a preferred first aggregate which are dimensionedin accord with U.S. Pat. No. 6,467,996, mentioned above. By analogy witha trickling bed filter, desired aerobic microbiological action isenhanced in aggregate, namely within pebble aggregate 36, which hasincreased surface area. When the wastewater exits the drainage unit andenters sand 42 and then soil 40, as is well known it will usually befurther microbiologically treated, according to conditions at thoselocations and the remaining activity of the wastewater.

Aggregate 26 provides structural integrity to drainage units of theprior art and of the present invention during use. That integrityincludes strength sufficient to resist the load of overlying soil andthings which traverse the soil surface. In this respect, the particlescomprising the larger exemplary bead aggregate 26 interlock with eachother better than do the smaller pebbles comprising aggregate 36. Thusthe aggregate 26 provides a drainage unit of the present invention withstrength and resistance to deformation during use. Having a relativelythin layer—and therefore relatively small amount—of pebbles, ascharacterizes the quilt of the present invention, will not significantlycompromise satisfactory structural performance of drainage units of thepresent invention.

The layers 32, 34 of quilt layer 30 are fastened to each other by one ormore means, such as a process selected from the group consisting ofstapling, sewing, ultrasonic welding, fusion welding, adhesive bonding,all of which methods are known in the art of fabricating plastic sheetstructures.

Other fastening or seam forming processes may be used, including thosewhich are known or are to be developed in the future. The exteriorsurface layer 32 is preferably comprised of a layer havingcharacteristics like barrier layers used on drainage units in the priorart. Its principle function is to keep the surrounding soil or othermedium from moving into the interstices of the aggregate 26 of theessential drainage unit. The interior or base layer 34 of a quiltpreferably is comprised of a coarser geotextile than is the cap layer 32of the quilt. In an example of the invention, an about 0.006 inch thickSpunbond polyester fabric having a Frazier Air Permeability of about 780cubic feet per minute per square foot at a pressure of 0.5 inch watercolumn may be used for the base layer 34 and a nonwoven polypropyleneneedle-punched geotextile having an ASTM D 4491 permittivity of about 2s⁻¹ may be used for the cap layer 32. Such exemplary base layer materialhas a lower permeability and is stiffer than the exemplary cap layermaterial. As used herein, the term geotextile refers to a fabric whichis water permeable unless otherwise stated.

As mentioned in the Background, typically wastewater flowing into adrainage unit that is part of a leaching system will contain suspendedsolids. Over time, the solids can accumulate and block flow through thepores of geotextile fabric barriers which are used on drainage units. Inthe invention, the first coarser layer of the quilt cooperates with thesecond finer layer of the quilt. Coarse particulates are caught by thefirst fabric layer 34, thus lessening the particulate loading on thesecond layer which will catch smaller particulates. The treatment anddegradation of the particulates is distributed between the first andsecond layers and the capacity of a drainage unit to handle a givenloading of suspended solids is increased, compared to a drainage unitwhich has an exterior surface comprised of one layer. Spacing betweenthe two layers is maintained by the presence of pebbles 36.Notwithstanding the benefits of using a combination of coarse and finepermeability materials in a quilt, in other embodiments of the inventionthe base layer and the cap layer may be of the same permeability. Asmentioned above, the finer pebble aggregate still provides an advantage.

Of course, where there are seams 44, 48, flow through the quilt will beimpeded, and such wastewater as passes through a seam will not encounterpebble aggregate. It is possible to construct a drainage unit like unit20 where there is no segmenting of the quilt, that is, where there is nocompartmentalization of the pebbles within the space between the baselayer and cap layer. But during shipping and handling of the drainageunit prior to installation, the pebbles might easily shift and becomeunevenly distributed around the circumference of the drainage unit,resulting in unpredictable performance. Quilting with segments avoidsthat possibility, and having seams is a necessary and useful tradeoff.

Whether a user wants a stiff unit or a bendable drainage unit depends onthe application. Most often it is desirable that drainage units bebendable along the lengthwise axis, so they fit readily in curvedtrenches. In a preferred embodiment such as shown in FIG. 1, thetransverse seams 48 which define the ends of rectangular shape segmentsare aligned with each other; and thus they provide circumferential bandlocations which facilitate ready lengthwise bending. The bands formed byaligned seams 48 help address any increase in lengthwise stiffeningwhich a drainage unit may have when there is a quilt, for instance aquilt comprised of whole-length strips as shown in FIG. 12, or forinstance when the rectangular quilt segments are not aligned but arestaggered as in common brickwork.

Since a quilt is made of flexible fabric and a quilt is curved as itforms the exterior of a drainage unit the dimensions of quilt segmentscan be distorted. There can also be gross distortion of the quilt at theends of a drainage unit where it is attached to itself and anyperforated pipe. Thus a reference herein to a quilt having certain shapesegments is a reference to the nominal shape of the segments whichcomprise the preponderance of the segments. Thus, for example, the term“rectangular” and variations should be applied reasonably whencharacterizing segment shapes.

Fabrication of Quilts

FIGS. 6-8 are fragmentary top views of quilts in the process of beingformed. They illustrate a portion of flat quilt having an edge 46, asthe quilt appears if it were laid on a flat surface prior to beingwrapped around the exterior of an essential drainage unit. The Figuresalso serve to illustrate ways of fabricating the quilt, which will bebetter appreciated from the description below relating to FIG. 9. FIG. 6shows a quilt with a rectangular segment pattern (in particular, asquare pattern) like that which characterizes quilt 30 of drainage unit20 in FIG. 1. FIG. 8 shows a quilt which has parallel rectangularsegments (or strips) that extend the length of the drainage unit, whenthe quilt is put in place. FIGS. 6-8 are discussed further below. FIGS.7, 7A and 7B show quilt embodiments having rounded or irregular shapequilt segments.

FIG. 9 is a perspective view, in part semi-schematic, illustrating someessential features of apparatus 18 and an associated manufacturingmethod that may be used for fabricating exemplary quilts 70, 70A, 70B,etc. which are rectangular in shape. Generally, the number 70 designatesa quilt when it is being fabricated or ready for incorporation into adrainage unit; and the number 30 designates that same item when it is apart of a drainage unit. (Those same categorizations apply to 70 and 30when they have prefixes, as in elements 170, 130, etc. in otherfigures.) FIG. 10 is a lengthwise elevation cross section of theapparatus 18 and shows a quilt being formed. FIG. 12 is a top view of atypical quilt product of apparatus 18, showing how the continuous stripof quilting which is produced by the machine may be cut at lines 68 toform rectangular quilts 70 ready for placement on an essential drainageunit. FIG. 13 illustrates how a rectangular quilt blanket 70 may bewrapped around the exterior of an essential drainage unit 16 to become aquilt 30.

Returning again to the machine and method illustrated by FIG. 9-11, thearrows show the motions of the elements of the apparatus and quiltcomponents. In the particular example shown, the rectangular quilts 70which are being produced have the elongated rectangular segment patternwhich is shown in FIG. 8. Geotextile fabrics 34 and 32 are provided asrespective pay-off rolls 54, 56, supported on trunnion, not shown. (Theterms geotextile and fabric are used interchangeably. A geotextile is awoven or non-woven textile product that is specially engineered for usein the exterior environment and when buried in soil.) The fabricatedquilt layer 30 is gathered as take up roll 64 which powered by a driver,not shown.

In operation of the apparatus 18, layer 34 is pulled lengthwise alongwork table 62 by rotation of take up roll 64. Pebbles 36 are depositedas a layer on the surface of fabric layer 34 by means of hopper 60 andassociated cog-feeder 66. Fabric layer 32 is drawn from roll 56 byvirtue of being seam-attached to layer 34, as will be described. Layer32 passes under idler roller 58, thereby forming a sandwich assemblycomprising the base layer 34 and cap layer 32 into which are depositedpebbles 36.

The assembly comprising the two geotextile layers passes by a pluralityof sewing heads 50 which form lengthwise seams 44, to make an exemplaryquilt pattern like that shown in FIG. 8. Sewing heads 50 are onlyschematically illustrated. They may be of a commercial type suited forthe thicknesses and materials being joined. In one mode of operation,the pebbles under the sewing heads are simply crushed by the sewingheads and associated feet or rollers. In another mode, hopper 66 isarranged so the pebbles are deposited at spaced apart locations acrossthe width of the machine; and thus there will be lengthwise runningchannels in the pebble layer where seams are wanted. In anotheralternative, plows create the channels.

Transverse seams 48, in particular seams 48A, 48B, are created bytraversing fastening heads 52 using stitching or one or more of thejoining methods mentioned elsewhere herein. Seam 48A defines the end onerectangular quilt 70A and seam 48B defines the beginning of the nextrectangular quilt. Sewing heads 52 are part of a flying assembly. Thatis, the heads 52 are attached to a mechanism (not shown) which moves theheads downstream at the speed of the moving fabrics 32, 34, when theheads are simultaneously moved transverse to the length of the quiltbeing formed. After the seams 48A, 48B are formed, the heads retreat tothe home position shown in FIG. 9, ready for further action when thedesired length of quilt passes by their home position.

Alternatively, the motion of the sandwich comprising the fabric layersand pebbles may be momentarily ceased while transverse seams 48A, 48Bare being formed. When the rectangular/square segment quilt patternshown in FIG. 1 and FIG. 6 is desired, the same kind of transverse head52 motion may be used, but more frequently.

The action of pebble feeder 66 may be intermittent, so there are regionsalong the length of moving fabric 34 where there are no pebbles, toenable more easy formation of the transverse seams. Plows or otherchannel making devices may be alternatively used to clear away pebblesand ease the fabrication of transverse seams.

FIG. 11 is a fragmentary portion of a modified FIG. 9 apparatus, showingsewing heads 50E which are staggered downstream along the length of worktable 62, which is the direction of downstream motion of the fabriclayers. The utility of this will be appreciated when forming the quiltillustrated in FIG. 7 is discussed.

As illustrated by FIG. 12, quilt accumulated on a take up roll isremoved from the machine 18 and subjected to a further manufacturingoperation: the quilt material is drawn from the roll and severed along aline 68, which runs in the space between the transverse seams 48A, 48Bto provide separate quilts 70 that may be wrapped around an essentialdrainage unit, as illustrated by FIG. 13 which is discussed below.

Referring again to the top views of FIGS. 6 to 8, the manner in whichsewing heads create seams is illustrated. In FIGS. 6 to 8 the segmentsare illustrated with paths direction of movement of the fabrics asindicated by arrow M is from right to left; that compares with left toright movement in FIG. 9. A portion of a quilt including side edge 46 isshown in each Figure.

In FIG. 8, quilt 70A has only lengthwise seams 44 which are formed byheads 50. In FIG. 6, quilt 70 has lengthwise seams 44 created by sewingheads 50 and transverse seams 48 created by heads 52.

In FIG. 7, quilt 70B has a combination of dominant circular segments 45in combination with scalloped edge segments 47. The motion of the sewingheads which forms the segments is more complex than in quilts withrectilinear segments. But the method illustrated avoids the mechanicalcomplexities associated with flying heads 52, or with stopping andstarting the quilt to make transverse seams. In the apparatusillustrated in FIG. 7, head 50A forms an outer seam along edge 46 of thequilt; head 50A is static relative to the width of the quilt. Typicalheads 50B, 50C, 50D and 50E translate transverse to the length of thequilt and direction of its movement relative to the heads, indicated byarrow M. Heads 50B and 50C move in a band BD1 to respectively createseams 44B and 44C. Heads 50D and 50E move in a band BD2 to create seams44D and 44E. (Seams are shown variously as dashed, solid single line,double line, etc. simply to enable distinguishing one seam from theother.) Other heads, which are not shown, form the other seams. Sincethe heads are staggered downstream, each head can oscillate transverselywithout interfering with the other head.

To recapitulate, heads 50B, 50C move within a band BD1, heads 50D, 50Emove with in BD2, etc. Said bands are regions running lengthwise alongthe nascent quilt. The motion of each head creates a serpentine seamwithin a respective band. In the FIG. 7 embodiment, seams within oneband intersect with each other to form generally circular segments 45.Seams within one band meet but do not cross the seams in the adjacentband.

FIG. 7A shows an embodiment of the invention which has similarities tothe embodiment of FIG. 7. Again, there is a multiplicity of heads, threeof which are shown creating a portion of nascent quilt 70C. Each ofheads 50F, 50G, 50H creates a respective serpentine seam 44F, 44G, 44Hin a respective band BD1, BD2, BD3. Oblong quilt segments 49 arepredominately created, along with half-oblong segments 51. Theserpentine seams within one band intersect but do not cross the seams inan adjacent band.

FIG. 7B shows another embodiment with some similarities to that of FIG.7A. Quilt 70D is formed with serpentine seams 44H, 44I and 44J.Exemplary bands BD1 and BD2 overlap, and the seams formed in one bandcross the seams in the adjacent band to create complex shape segments.Still other variations of quilts having different intersections ofserpentine bands may be constructed. In the foregoing descriptionsrelating to seam forming, it will be appreciated that the motion betweenthe sewing heads and the fabric is relative. Thus, while static sewingheads have been shown, the invention can be carried out by holding thefabric stationary on a table and moving the heads. While sewing headswhich provide stitching in the fabric have been described, other meansfor joining the fabric may be employed as equivalents, includingstapling, ultrasonic or other melt-bonding, adhesive bonding, and soforth, each having an associated head for effecting the particularfastening.

The foregoing method invention may be generally described as follows: Amethod for making a drainage unit having a quilted surface comprisesfirst forming a quilt by sandwiching pebble aggregate between a firstsheet and a second sheet, creating seams by sewing or equivalent means,so the sheets are fastened to along the length of the fabric; andcreating transverse seams which define the ends of rectangular quilts,and depending on the segments being formed, rectilinear segments.Rectangular quilt pieces are then wrapped around an essential drainageunit and affixed in place, to form an invention drainage unit having aquilt surface. Quilts may have rectilinear segments or complexly curvedsegments. In another kind of quilt, serpentine lengthwise seams areformed within parallel lengthwise band regions of the nascent quilt and(a) the seam in one band intersects a seam in the same band or (b) aseam in one band intersects the seam in an adjacent band or (c) a seamin one band crosses the seam in an adjacent band. With the scope ofinvention, other segment shapes may be formed than have beenexemplified.

FIGS. 15-18 illustrate an alternative apparatus and method forfabricating quilt. Various actuators and controls which make thecomponents of the system move are not shown but will be understood bythe artisan. Generally, in the apparatuses of FIG. 15 and FIG. 18 twosheets of fabric are mated and fastened to each other to form a sheetstructure which has vertically disposed channels analogous to theprocess described in connection with FIG. 9. The quilt 170, beingformed, moves vertically downward during the manufacturing process.Aggregate 36 is dropped into vertical channels and horizontal seams arecreated, so a multiplicity of rectangular quilt segments 43A are formed.

FIG. 15 is vertical cross section through a portion of the apparatus118. Arrows show the motion of the parts of the apparatus and sheet andquilt. A portion of an exemplary quilt 170 which is produced by theapparatus 118 is shown in FIG. 17. The apparatus is shown in simplifiedform, i.e., at only one vertical plane. The more complex configurationof the whole apparatus will be understood in the context of thedescription associated with FIGS. 9 to 10A and the following. Ultrasonicwelding is referred to the exemplary fastening means; but any of themeans described elsewhere herein may alternatively be used.

Fabric which forms quilt layers 32, 34 is drawn from spools which arenot shown. Fabric which comprises sheet/layer 32 runs over roller 76. Asshown in the partial cross section of FIG. 16, roller 76 has a groovedsurface; thus the sheet 32 is contoured so it has lengthwise runningpeaks and valleys as it runs over the roller. Fabric which comprisessheet/layer 34 is drawn over roller 78 and mated vertically withcontoured sheet 32 to form a geotextile assembly. An ultrasonic welderis shown schematically. It comprises which a horn 151 (i.e., an elementwhich applies ultrasound waves to the geotextile layers) and anassociated anvil 150 which is a wheel-like element. The ultrasonicwelder creates a vertical seam 44 where a valley of the layer 32contacts the layer 34. The seam in combination with an adjacent seamdefines a vertical channel of the geotextile assembly.

In the full apparatus, there is a multiplicity of vertical seam welders.They are spaced apart in a direction which is perpendicular to the planeof the FIG. 15 illustration. Thus, a multiplicity of vertical seams 44and associated vertical channels are formed in a geotextile assembly,analogous to how the seams and channels are formed in making quilt 70Ashown in FIG. 9.

A multiplicity of tubes 82, one of which is shown, feed aggregate 36from hopper 80 into each vertical channel. As the being-formed quiltmoves vertically downwardly, indicated by arrow Q, spaced-aparthorizontal seams 48 are formed. Ultrasonic welder horn 86 which has anassociated anvil 84B periodically moves toward the geotextile assembly,and then away as indicated by arrow M, while traversing the geotextileassembly to form a horizontal seam 48. Thus the vertical channels areconverted into rectangular aggregate-filled segments 43A of quilt 170.In the manufacturing process, flow of aggregate through the tube 82 ispreferably periodically interrupted, so that a horizontal weld 48 can bemade just above the elevation of the elevation of the just-depositedaggregate.

FIG. 18 shows apparatus 218 which is a modification of the apparatus118. Apparatus 218 comprises a subsystem that quickly deposits apredetermined amount of aggregate into a vertical quilt channel, afterwhich a horizontal weld is made just above the elevation of theaggregate.

In the apparatus of FIG. 18, the way of mating the sheets 32, 34 andforming the vertical channels is the same as described for FIG. 15. As astarting point, assume there is already a present horizontal weld seam48, at the top of segment 43A of quilt 170. Aggregate 36 is thendeposited into the vertical channel above the seam by means of tube 182which extends downwardly from base plate 90. Quilt 170 is then moveddownwardly, and a second seam (not shown) is formed at the elevationwhich just above the height of the just-deposited aggregate. Thatcreates a new segment 43A. The second seam defines the bottom of thenext to-be-formed segment. More aggregate is deposited in the channelabove the second seam as the being-formed quilt moves downwardly; thenanother horizontal seam is made, and so forth.

In apparatus 218 a predetermined amount of aggregate is delivered bymeans of a mechanism comprising shuttle 88. The shuttle moves left-righton base 90 as indicated by arrow N in FIG. 18. Shuttle 88 has two spacedapart vertical cavities 92A, 92B. Stationary hoppers 80A and 80B arepositioned above the shuttle so that each cavity 92A, 92B may be filledwith aggregate 36 from respective hoppers 80A, 80B, when the shuttleposition locates a cavity beneath a hopper.

In FIG. 18, shuttle 88 is at its far right position and vertical cavity92B has just been filled by hopper 80B. Vertical cavity 92A is at thesame time positioned over spout 182. A periodic compressed air jet,indicated by arrow P, emanates from nozzle 94. The air jet applies forceto aggregate 36A which is in cavity 92A so, as shown, the aggregatemoves down spout 182 and into the vertical channel of the quilt 170being formed. When the aggregate is in place within the quilt channel,quilt 170 moves vertically down as indicated by arrow Q, momentarilystopping while horizontal welder 84 moves toward the quilt to seal thesheets 32, 34 to each other just above the aggregate 36A, thus creatinga new segment 43A. At the same time, shuttle 88 moves laterally to theleft so that cavity 92B is positioned over the tube 182 and cavity 92Ais positioned under hopper 80A. The blowing, filling, welding andshuttling steps are repeated again and again. In this way, quilt can bemanufactured in a rapid and economic way. Other means for delivering apredetermined amount of aggregate 36A may be employed. For instance, asknown in the art, weighing machines having discharge bins may be used todeliver pellets to a tube like tube 182 that extends into the verticalchannel of a quilt being formed; or machines which count the number ofpellets being fed past a point by a vibratory feeder may be used.

An essential drainage unit 16 for receiving a quilt may be fabricated bymeans which have been commercially employed heretofore by manufacturersof drainage units. Reference may be made to U.S. Pat. Nos. 5,015,123,5,154,543, and 5,535,499, the disclosures of which are herebyincorporated by reference. Essential drainage units may be made by othermeans and may have constructions different from those shown in theforegoing patents.

The next step is to apply a quilt to the essential drainage unit 16, tomake an embodiment of drainage unit 20 of the present invention. A quilt70 is fabricated using a method described above, or another method.

In one approach, illustrated in part by FIG. 13, the quilt 70 has alength approximating the length of the essential drainage unit whichwill be encased in the quilt and the width of the quilt is preferablyabout equal to, more preferably greater than, the circumference of theessential drainage unit to which the quilt is applied. FIG. 13 showsdrainage unit 120 which in the process of being formed by wrapping quilt70 around the around the exterior of essential drainage unit 16.Preferably the width of the quilt will be such that lengthwise edge 46Awill extend beyond the edge 46 when the quilt is wrapped around theessential drainage unit 16, so there is an about 4 inch overlap of thequilt upon itself. Alternately, the lengthwise edges 46, 46A of thequilt 70 may be secured to each other at a seam which runs lengthwisealong the length of the drainage unit. A quilt may be attached to itselfby sewing, stapling, gluing, ultrasonic welding, or other meansdescribed elsewhere herein or known in the art. Thecircumferential-running quilt edges, which are in proximity to the endsof the essential drainage unit, where a center pipe 22 is exposed ifpresent, may be gathered together about the pipe with a cord or clamp orstitching, etc.; or the edges may be secured to themselves or even leftunsecured or un-gathered.

In still other alternative ways for fabricating drainage units, a quiltmay be secured in place around the outer surface of the essential unitby sewing or adhering of the quilt to the sleeve 26. Or the quilt may besecured to the circumference of an essential drainage unit by means ofcircumferential cord or strapping which runs around the exterior of thequilt. In this embodiment, with reference to FIG. 1, a multiplicity ofstraps may be run around the exterior of the quilt, parallel to thealigned-seams 48. See also U.S. Pat. No. 8,256,990 of Koerner, mentionedabove, for how straps may be used.

FIG. 19 is a perspective partial-cutaway view, and FIG. 19A is a partialtransverse cross section, of a drainage unit 320 where quilt 30 issecured to the exterior of the essential drainage unit by second sleeve55 of netting. As in other figures, the essential drainage unit 16comprises aggregate 26 contained by first netting-sleeve 24. Preferably,the quilt is wrapped around the essential drainage unit so it overlapsitself by 2 to 4 inches, in the manner described in connection with FIG.13. The second or outer sleeve 55 may be put in place by different ways.In one embodiment the sleeve is provided in the form a tube or bag-likestructure which is slid lengthwise along the exterior surface of thequilt while the quilt is temporarily secured in place.

As mentioned above, with respect to making an essential drainage unit16, reference may be made to the apparatus and methods of making whichare described or obvious from U.S. Pat. Nos. 5,657,527 and 6,173,483 ofHouck et al., the disclosures or which are hereby incorporated byreference. FIG. 22 is a cross section through elements of prior artapparatus. A sleeve of netting 30 drawn from the exterior of a hollowcylindrical mandrel 59, through which a perforated pipe 22 is thrustlengthwise. The rucked netting 30A is drawn off the mandrel by the pipe22 to which it is tied by strap 57. Bead aggregate is blown down themandrel interior as indicated by the arrow, to fill the space betweenthe sleeve and the perforated pipe. FIG. 20 shows how those sameprinciples may be used to make a drainage unit 420. Quilt 30 in the formof a sleeve which is on the exterior of mandrel 59 is initially securedto the end of perforated pipe 22 by tie-wrap 57. Movement of the pipedownstream as indicated by the arrow draws the quilt sleeve from the end65 of mandrel 59 while aggregate 26 is blown down the annular space 63between the perforated pipe 22 and mandrel. When the desired length ofdrainage unit is achieved, the upstream end of the quilt is secured tothe upstream end of the perforated pipe.

It will be appreciated that nicking quilt on the mandrel may not bereadily done, given its bulk compared to a netting sleeve, and thus thequilt may be formed into a sleeve as it approaches the mandrel. FIG. 21is a simplified illustration which shows mandrel 59 and perforated pipe.Quilt 70 in the form of sheet is converted into a sleeve that runs alongthe exterior of mandrel 59. The quilt sheet 70 is drawn from a spool orother source (not shown) and curved upon itself by an unshown collar sothat it assumes the form a cylinder circumscribing the exterior ofmandrel 59. A fastening device 67, such as a sewing head or stapler orwelder, secures the edges 46, 46A of the quilt sheet 70 to each other sothat the sheet becomes cylindrical sleeve quilt 30. The mandrel in theforegoing apparatus may have other than horizontal orientation in otherembodiments of the invention. Technology which may be employed in theforegoing process or in alternative ways may be ascertained in U.S. Pat.Nos. 7,178,224, 7,475,477, and 7,600,308 all of Bussey, Jr. et al., thedisclosures of which are hereby incorporated by reference.

Further Embodiments of Drainage Units

FIG. 13A shows another embodiment of drainage unit 220, where quilt 70only runs around a portion of the circumferential exterior of theessential drainage unit 16. Quilt 70 may be secured to the drainage unitby fastening to the sleeve netting 24, by stitching, stapling, fusion,adhesive, etc., or by a second netting sleeve like sleeve 55 describedin connection with FIGS. 19 and 19A. In the generality of the inventiona perforated pipe running through the aggregate is optional, althoughpreferred. FIG. 13A also shows that exemplary unit 220 has no lengthwiseperforated pipe.

As shown in FIG. 3, the base layer 34 of a quilt 30 of drainage unit 20is in contact with the netting of sleeve 24 and aggregate 26 that iscontained by the netting, given the large openings in the netting. In analternative embodiment drainage unit 20A, shown in FIG. 5, there is afurther layer 28 between the sleeve 24 and the quilt base layer 34.Layer 28 may be a fibrous mass, or a disorganized spaghetti-likestructure as characterizes the commercial product Enka mat, or a geonetstructure (a coarse, heavy duty netting, referred to further below).Layer 28 may provide structural stiffness to drain 20A (when that isdesired) as well as providing a zone for further treatment ofwastewater. Layer 28 spaces apart the base layer 34 from the aggregatewhich lies within the interstices of netting 24, lessening any maskingof the openings in layer 34 which might result when the layer contactsthe aggregate.

FIG. 14 shows a transverse cross section through exemplary drainage unit230 which comprises aggregate, pipe, and netting of an essentialdrainage unit 16. An essential drainage unit 16 is surrounded by one ormore layers of geonet 72, that is, coarse mesh plastic material. Geonet72 is overlaid by geotextile fabric 74, such as fabric similar to thefabric of layers 32, 34 of an exemplary quilt. (When such kind of fabrichas been placed on the exterior of an essential drainage unit in theprior patent art, it has been called a barrier.) Unit 230 does notcomprise a quilt. If a quilt was substituted for layer 74, the productwould be like that shown in FIG. 5.

A preferred geonet useful in this embodiment and the embodiment of FIG.5 is Transnet Geonet 220, made of high density polyethylene. Thepreferred geonet layer has a thickness of about 0.22 inches and diamondshape mesh openings of about 0.4 by 0.7 inches. The material has an openarea of 65-70 percent. The geonet layer 72 spaces apart the fabric 74from outer surface of the essential drainage unit and facilitates flowthrough the fabric 74. In the absence of the geonet, the outer fabriccontacts the aggregate, since a typical sleeve netting allows suchcontact. That contact can result in masking, that is, the creation ofregions where flow through the outer fabric is blocked, possibly to theextent that 45 to 50 percent of the fabric openings may be masked. Thegeonet has openings which are intermediate in size between the openingsof the first netting sleeve 16 and the openings of the geotextile of thequilt.

The invention, with explicit and implicit variations and advantages, hasbeen described and illustrated with respect to several embodiments.Those embodiments should be considered illustrative and not restrictive.Any use of words such as “preferred” and variations suggest a feature orcombination which is desirable but which is not necessarily mandatory.Thus embodiments lacking any such preferred feature or combination maybe within the scope of the claims which follow. Persons skilled in theart may make various changes in form and detail of the inventionembodiments which are described, without departing from the spirit andscope of the claimed invention.

What is claimed is:
 1. A drainage unit, for receiving and collectingwater when buried in soil or other particulate material, having alength, a diameter, a nominally cylindrical exterior, and opposing ends,comprising: a generally cylindrical mass of first aggregate; and, aquilt made of water permeable geotextile running around all or part ofthe circumference of said first aggregate mass, the quilt comprised of amultiplicity of interconnected segments, each segment comprising aninternal cavity containing a second aggregate, wherein the secondaggregate has an average particle size which is smaller than the averageparticle size of the first aggregate.
 2. The drainage unit for receivingand collecting water when buried in soil or other particulate material,having a length, a diameter, a nominally cylindrical exterior, andopposing ends, comprising: a generally cylindrical mass of firstaggregate; and, a quilt made of water permeable geotextile runningaround all or part of the circumference of said first aggregate mass,the quilt comprised of a multiplicity of interconnected segments, eachsegment comprising an internal cavity containing a second aggregate;wherein the quilt is comprised of a first layer of geotextile which isfastened to a second layer of geotextile at seams formed by a processselected from the group consisting of ultrasonic welding, stitching,adhesive bonding, fusion welding, stapling and combinations thereof;wherein the first layer of the geotextile faces the cylindrical mass ofaggregate and the second layer of geotextile faces the exterior of thedrainage unit, wherein the first layer has a water permeability which isdifferent from the water permeability of the second layer.
 3. Thedrainage unit of claim 1 wherein the second aggregate comprisesparticulate having an average particle size which is less than half theaverage particle size of the particulate of the first aggregate.
 4. Thedrainage unit of claim 3 wherein the first aggregate has an averageparticle size which is greater than about one inch and the secondaggregate has an average particle size which is about one-quarter inch(0.6 cm) or less.
 5. The drainage unit of claim 1 further comprising aperforated pipe running lengthwise within the first aggregate, forflowing water within the drainage unit, the pipe having opposing endsone of which is exposed at each of the opposing ends of the drainageunit, wherein the quilt is fastened to each pipe opposing end.
 6. Thedrainage unit of claim 1 further comprising a sleeve of netting runningaround the cylindrical mass of aggregate, underneath the quilt.
 7. Thedrainage unit of claim 2 wherein the water permeability of the firstlayer is higher than the water permeability of the second layer.
 8. Thedrainage unit of claim 1 further comprising: (a) a first sleeve ofnetting running around the cylindrical mass of first aggregateunderneath the quilt; and (b) a second sleeve of netting running aroundthe quilt, for holding the quilt in position upon the first sleeve ofnetting and mass of first aggregate.
 9. The drainage unit of claim 1wherein the quilt comprises (a) a base layer of geotextile which is incontact with either the first aggregate mass or with an optional sleeveof netting that contains the first aggregate mass; and (b) a cap layerof geotextile which faces toward the exterior of the drainage unit;wherein the base layer has a higher water permeability than the caplayer, and wherein the cap layer is more undulating than the base layer.10. The drainage unit of claim 1 wherein the quilt comprises (a) a caplayer of geotextile which is in contact with either the first aggregatemass or with an optional sleeve of netting that contains the firstaggregate mass; and (b) a base layer of geotextile which faces towardthe exterior of the drainage unit; wherein the cap layer has a higherwater permeability than the base layer, and wherein the cap layer ismore undulating than the base layer.
 11. The drainage unit of claim 1wherein the quilt comprises two layers of geotextile fastened to eachother at seams which define quilt segments, each layer undulating as aneffect of the seams and one layer presenting the exterior surface of thedrainage unit; wherein the first layer has a first water permeabilityand the second layer has a second water permeability which is less thansaid first water permeability.
 12. The drainage unit of claim 1 whereinthe quilt has a preponderance of segments which are shaped as one oflengthwise strip segments, rectangular segments, circular segments, orcurved edge segments.
 13. The drainage unit of claim 12 wherein thequilt has a multiplicity of rectangular segments defined by acombination of first group of seams which run lengthwise along thedrainage unit and a second group of seams which run transverse to thelength of the drainage unit; and wherein the seams of the second groupare aligned to form circumferential bands, the bands providingpreferential locations for lengthwise bending of the drainage unit. 14.A drainage unit, for receiving and collecting water when buried in soilor other particulate material, having a length, a diameter, a nominallycylindrical exterior, and opposing ends, comprising: a generallycylindrical mass of first aggregate; and, a quilt made of waterpermeable geotextile running around all or part of the circumference ofsaid first aggregate mass, the quilt comprised of a multiplicity ofinterconnected segments, each segment comprising an internal cavitycontaining a second aggregate; wherein the quilt comprises two layers ofgeotextile fastened to each other at seams which define quilt segments,each layer undulating as an effect of the seams and one layer presentingthe exterior surface of the drainage unit, wherein the undulation of theexterior surface area layer provides the drainage unit with a surfacearea per unit length that is greater than the surface area of a sameexterior dimension drainage unit having a smooth surface made of thesame geotextile which comprises the exterior surface layer.
 15. Thedrainage unit of claim 14 wherein said surface area per unit length ofthe drainage unit is at least about 2 percent greater than the surfacearea per unit length of a drainage unit of a same exterior dimensiondrainage unit having a smooth surface made of the same geotextile whichcomprises the exterior surface layer having the same diameter and asmooth exterior surface.
 16. The drainage unit of claim 15 furthercomprising a perforated pipe running lengthwise through the mass ofaggregate.
 17. The drainage unit of claim 1 wherein the quilt runsaround the exterior of drainage unit and overlaps on itself, optionallywith a lengthwise seam in vicinity of the overlap.
 18. The drainage unitof claim 1 having a diameter between about ten inches (25.4 cm) andabout twelve inches (30.5 cm), wherein the thickness of the quilt isbetween about three eighths inch (1 cm) and about five eighths inch (1.6cm).
 19. A leaching field comprised of a multiplicity of interconnecteddrainage units of claim 1 which are buried in soil.
 20. A leaching fieldcomprised of a multiplicity of interconnected drainage units of claim 2which are buried in soil.
 21. The drainage unit of claim 1 wherein thequilt comprises (a) a base layer of geotextile which is in contact witheither the first aggregate mass or with an optional sleeve of nettingthat contains the first aggregate mass; and (b) a cap layer ofgeotextile which faces toward the exterior of the drainage unit; whereinthe base layer has a higher water permeability than the cap layer, andwherein the cap layer is more undulating than the base layer.
 22. Thedrainage unit of claim 1 wherein the quilt comprises (a) a cap layer ofgeotextile which is in contact with either the first aggregate mass orwith an optional sleeve of netting that contains the first aggregatemass; and (b) a base layer of geotextile which faces toward the exteriorof the drainage unit; wherein the cap layer has a higher waterpermeability than the base layer, and wherein the cap layer is moreundulating than the base layer.